You also have to override/implement the follwoing methods:

public override string GetUserUniqueName( HttpContext context )
this methods provides access to the UserID of the currently logged-in user.
If this method returns NULL then you are asked for login, else you can procceed with a "scient" login.

In order to have a "pretty" name of the user you have to implement/override:
public override string GetUserDisplayName( string useruniquename )
this method takes the UserID as param and retruns string presentation of the user. So here you can add the first&last name...

Hope this helps.
Diman